Method and apparatus for cutting semiconductor wafers

ABSTRACT

Improperly mounted wafer saw blades can damage wafers cut or diced with the blades. Embodiments of this invention employ sensors to measure a distance to the blade to help indicate if the blade is improperly mounted. In one method of the invention, a the distance to the blade face is measured as the blade is rotated and a variance in this measured distance is determined. If the variance is no greater than a predetermined maximum, the blade may be used to cut the wafer. In one apparatus of the invention, a wafer saw include a blade and a sensor. The sensor is adapted to monitor a distance to a face of the rotating blade. A processor coupled to the sensor may indicate if the distance to the face of the blade as it rotates deviates too far from a baseline position of the blade face.

TECHNICAL FIELD

[0001] The present invention generally relates to devices and methodsfor cutting microelectronic devices, such as in dicing semiconductorwafers into individual dies.

BACKGROUND

[0002] An individual microelectronic component or die is usually formedfrom a larger substrate, typically a semiconductor wafer. Wafers mostcommonly are formed primarily from silicon, although other materialssuch as gallium arsenide and indium phosphide are also sometimes used.Semiconductor wafers have a plurality of dies arranged in rows andcolumns. Typically, the wafer is sawed or “diced” into discrete dies bycutting the wafer along mutually perpendicular sets of parallel lines or“streets” lying between the rows and columns.

[0003] In a typical dicing operation, a semiconductor wafer is attachedto a carrier, such as by use of an adhesive, and the carrier is mountedon a table of wafer saw. The wafer saw includes a rotating dicing bladewhich is attached to a rotating spindle. The dicing blade has aperipheral cutting edge which may be coated with diamond particles orother abrasives to assist in cutting the semiconductor wafer. As theblade of the wafer saw is rotated, it cuts at least partially throughthe thickness of the wafer and is carefully guided along the streetsbetween adjacent dies. The blade may be guided along these streets bymoving the blade relative to the wafer, by moving the table of and thewafer relative to the blade, or by moving both the table and the blade.

[0004] If a blade is not precisely mounted on the spindle, theperipheral edge of the rotating blade can trace an irregular path withrespect to the axis of rotation of the spindle. Commonly, a blade willbe mounted with a flat blade surface clamped flush against a flatsurface of a mounting hub carried by the spindle. If the blade is notproperly clamped against the hub, any play in the attachment of theblade to the spindle may cause the peripheral cutting edge of the bladeto oscillate or waver irregularly. Sometimes a foreign particle canbecome wedged between the mounting hub and the face of the blade or themounting hub or the blade may have a burr on its surface. Such a foreignparticle or burr can cause the blade to be mounted at an angle. As theshaft is rotated, the path scribed by the peripheral cutting edge of theblade will wobble.

[0005] Wavering of the blade as the shaft is rotated can cause the bladeto deviate outside the intended street on the wafer, damaging dies onone or both sides of the street. Semiconductor wafers also tend to besomewhat brittle. A wavering blade can cause chipping of the surface ofthe wafer, damaging dies adjacent to the street even if the blade stayswithin the proscribed width of the street.

[0006] The difficulties associated with properly mounting dicing bladesis increasing as the semiconductor industry moves toward dual-bladewafer saws. There are two varieties of dual-blade wafer saws on themarket today—dual spindle saws (with parallel, side-by-side spindles)and twin spindle saws (with opposed, axially aligned spindles). One suchtwin spindle wafer saw is shown in FIG. 3 of U.S. Pat. No. 6,006,739,the entirety of which is incorporated herein by reference. Typically,such twin spindle dual-blade wafer saws simultaneously cut the surfaceof the semiconductor wafer along parallel lines using a pair of paralleldicing blades. The two blades typically have the same diameter and arerotated about a common rotation axis so they will cut the wafer to thesame depth. With commercially available dual-blade wafer saws, theoperator's access to the area where the blades are mounted is somewhatlimited. It is often difficult for the operator to view the bladesedge-on and the operator frequently must mount blades looking along orparallel to the axis of rotation. This makes it difficult for theoperator to see the mounting hubs to which the blades are beingattached, leading to errors in mounting the blades. In addition, it isdifficult to visually confirm that both blades are properly mounted. Ahighly-skilled, experienced operator can sometimes observe unacceptablewobbling of a cutting blade by watching the blade as it rotates. Thisvisual observation is made more difficult if the operator is only ableto watch a face of the blade instead of the edge of the blade. Indual-blade saws, an operator's view of the front blade is largelylimited to watching the face of the rotating blade and view of the rearblade is usually greatly hindered, if not completely blocked, bysuperimposition of the front blade between the operator and the rearblade.

SUMMARY

[0007] Embodiments of the present invention provide methods useful incutting a semiconductor substrate, e.g., a semiconductor wafer, andsemiconductor wafer saws. One embodiment of the invention provides amethod for cutting a semiconductor substrate wherein the semiconductorsubstrate is positioned with respect to a blade of a saw. The blade isrotated in a first spaced position wherein a peripheral cutting edge ofthe blade is spaced from the semiconductor substrate. A distance to aface of the blade is measured as the blade is rotated in the firstspaced position. A first variance in the measured distance is determinedas the blade is rotated. If the first variance is no greater than apredetermined maximum variance, the semiconductor substrate is contactedwith the peripheral cutting edge of the blade. The blade may betranslated with respect to the semiconductor substrate to cut at leastpartially through the semiconductor substrate. If so desired, the methodmay further include terminating rotation of the blade if the firstvariance is greater than the predetermined maximum variance. Oneadaptation of this embodiment includes positioning the blade in a secondspaced position after cutting the semiconductor substrate. Theperipheral cutting edge of the blade is spaced from the substrate whenthe blade is in the second spaced position. The blade is rotated in thesecond spaced position without cutting the semiconductor substrate, thedistance to the face of the blade is measured as the blade is rotated inthe second spaced position, and a second variance is determined.

[0008] Another embodiment of the invention provides a method ofoperating a semiconductor substrate saw which includes rotating a bladeof the saw without contacting the blade with a flow of liquid. Adistance to a face of the blade is monitored as the blade rotates. Afirst baseline distance to the face of the blade and a first deviationfrom the baseline distance are determined. An error is indicated if thefirst deviation is greater than a predetermined maximum deviation. Onlyif the error is not indicated, a first cut at least partially through asemiconductor substrate is made with the blade while contacting theblade with a flow of liquid, such as a cooling liquid.

[0009] A method of exchanging a blade of a semiconductor substrate sawis provided in accordance with another embodiment of the invention. Inthis method, a used blade is removed from a blade mount carried on ashaft of the saw. A new blade is mounted on the blade mount and the newblade is rotated prior to contacting a semiconductor substrate with thenew blade. Prior to contacting the semiconductor substrate with the newblade, a distance to a face of the new blade is monitored as the bladerotates, a baseline distance to the face of the blade and a deviationfrom the baseline distance are determined, and an error is indicated ifthe deviation exceeds a predetermined maximum deviation. Only if theerror is not indicated, a cut is made at least partially through thesemiconductor substrate with the blade.

[0010] Another embodiment provides a method of exchanging a blade of amultiple-blade saw which includes a used first blade and a second blade,which may also be a used blade. The used first blade is carried on afirst shaft for rotation with the first shaft and the second blade iscarried on a second shaft for rotation with the second shaft. The usedfirst blade is removed from the first blade mount and a new first bladeis mounted on the first blade mount. The new first blade is rotated in afirst position and a distance from a first sensor to a face of the newfirst blade is monitored as the new first blade rotates in the firstposition. The first sensor is associated with the second shaft. Anindication is made whether a first variance in the monitored distance asthe new first blade is rotated exceeds a predetermined maximum firstvariance. If the first variance is not greater than the maximum firstvariance, a semiconductor substrate may be contacted with the new firstblade and with the second blade. This method may further comprise movingthe second shaft and the first sensor laterally with respect to thefirst shaft, thereby changing the distance from the first sensor to theface of the new first blade.

[0011] Another embodiment of the invention provides a semiconductorwafer saw. The saw includes a carrier for a microelectronic workpieceand a driver. A first shaft is coupled to the driver and extendsopposite the carrier. The first shaft has a first axis. A first blademount is carried adjacent an end of the shaft for rotation with thefirst shaft and a first blade is carried by the first blade mount forrotation with the first blade mount. The first blade has a face andperipheral cutting edge. A sensor is spaced from the first blade and isoriented toward the face of the first blade. The sensor maintains afixed angular position with respect to the first axis as the first bladeis rotated with the shaft and is adapted to measure a distance to theface of the first blade. A processor is operatively coupled to thesensor. The processor is adapted to indicate if the distance to the faceof the first blade deviates more than a predetermined permitteddeviation from a baseline distance to the face of the first blade as theblade rotates.

[0012] Yet another embodiment of the invention provides an alternativesemiconductor wafer saw which includes multiple blades. In particular,this wafer saw includes a carrier for a microelectronic workpiece. Afirst spindle extends opposite the carrier and has a first axis. A firstblade is carried by the first spindle for rotation therewith and thefirst blade has a face and a peripheral cutting edge. A second spindleextends opposite the carrier and has a second axis. A second blade iscarried by the second spindle for rotation therewith and the secondblade has a face and a peripheral cutting edge. A first sensor iscarried by the second spindle and adapted to measured a first distanceto the face of the first blade. The first sensor maintains a fixedangular position with respect to the first axis as the first bladerotates about the first axis. A second sensor is carried by the firstspindle and is adapted to measure a second distance to the face of thesecond blade. The second sensor maintains a fixed angular position withrespect to the second axis as the second blade rotates about the secondaxis. A processor is operatively coupled to the first and secondsensors. The processor is adapted to indicate if variation of the firstdistance as the first blade rotates exceeds a predetermined maximumfirst variation and to indicate if variation of the second distance asthe second blade rotates exceed a predetermined maximum secondvariation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is schematic side view of a semiconductor substrate saw inaccordance with one embodiment of the invention.

[0014]FIG. 2 is a schematic isolation view of the encircled portion ofFIG. 1.

[0015]FIG. 3 is a schematic elevation view taken along line 3-3 in FIG.1.

[0016]FIG. 4 is a graph schematically illustrating output of the sensorof FIG. 1.

[0017]FIG. 5 is a schematic side view of a semiconductor substrate sawin accordance with an alternative embodiment of the invention.

[0018]FIG. 6 is a schematic top view of the semiconductor substrate sawof FIG. 5.

DETAILED DESCRIPTION

[0019] Various embodiments of the present invention providesemiconductor substrate saws and methods for operating such saws to cutsemiconductor substrates. The following description provides specificdetails of certain embodiments of the invention illustrated in thedrawings to provide a thorough understanding of those embodiments. Itshould be recognized, however, that the present invention can bereflected in additional embodiments and the invention may be practicedwithout some of the details in the following description.

[0020] Single Blade Saw

[0021]FIG. 1 schematically illustrates a semiconductor substrate saw 10in accordance with one embodiment of the invention. This saw 10 includesa wafer table 14 which can be used to support a wafer 12. In oneembodiment of the invention, the wafer table 14 is rotatable andtranslatable in a fixed horizontal plane. Such wafer tables andmechanisms for controlling their movement are well known in the art andneed not be discussed in detail here.

[0022] The saw 10 may also include a support 20 which is positionedadjacent the wafer table 14. The support 20 can take any desired form.In FIG. 1 the support 20 is schematically shown as an upright structureextending vertically from a position adjacent the table 14, but anystructure which properly positions the blade 40 with respect to thewafer 12 will suffice. The support 20 in FIG. 1 is shown as enclosing adriver 22. The driver 22 is operatively coupled to a spindle 30 torotate the spindle 30 about its rotational axis A-A. Any suitable driver22 may be employed. In one embodiment, the driver 22 is an electricmotor which can be electronically controlled by a processor 60.

[0023] The spindle 30 may be carried by the support 20 in any desiredfashion. In certain embodiments, the spindle 30 is movable with respectto the support along one or more axes. In one such embodiment, thespindle 30 is adapted to move toward the wafer table 14 and away fromthe wafer table 14 under control of the processor 60. For the wafer saw10 of FIG. 1 wherein the wafer table 14 is generally horizontal, thismotion of the spindle 30 may comprise substantially vertical movement.The spindle 30 may also be adapted to extend outwardly from and retractinwardly toward the support 20, such as by moving laterally generallyalong the rotational axis A-A of the spindle 30. In the illustratedembodiment, the rotational axis A-A is substantially parallel to thehorizontal plane of the wafer table 14 and the spindle moveshorizontally along this axis A-A.

[0024] Any suitable spindle 30 may be employed. In one embodiment, thespindle 30 comprises a shaft 32 which may be coupled to the driver 22. Amounting hub 34 having a mounting face 35 may be carried adjacent an endof the shaft 32 spaced away from the support 20. The mounting face 35should be substantially planar and may be polished to a smooth finish.The mounting face 35 of the mounting hub 34 should have a knownorientation with respect to the rotational axis A-A of the spindle 30.Preferably, the face 35 is substantially perpendicular to the rotationalaxis A-A.

[0025] The spindle 30 may include a mounting mechanism for firmlymounting a blade 40 against the mounting hub 34. This mounting mechanismmay take any suitable form. In FIGS. 1 and 2, the mounting mechanism isschematically illustrated as a retaining nut 36. The retaining nut 36 orother mounting mechanism is adapted to releasably retain a blade 40 onthe spindle 30. The retaining nut may engage an outer face 44 of theblade 40 and tightly clamp a mounting face 42 of the blade 40 againstthe mounting face 35 of the mounting hub 34. In ordinary operation, theportion of the mounting face 42 of the blade 40 covered by the mountinghub 34 will have a smooth, flat surface which is adapted to mate flushagainst the mounting face 35 of the mounting hub 34.

[0026] Any conventional semiconductor substrate cutting blade may beused as the blade 40. As noted previously, many such cutting bladesinclude a peripheral edge 46 adapted to cut the wafer 12 or othersemiconductor substrate. A wide variety of such blades 40 arecommercially available.

[0027] In operating a conventional wafer saw, the blade 40 and the wafer12 are contacted with a flow of a cooling liquid, such as deionizedwater, to minimize damage to the wafer 12 due to localized overheating.In the saw 10 of FIG. 1, this flow of water or other cooling liquid maybe delivered through a water line 16. To prevent the water from sprayingas the blade rotates and to help protect the blade from inadvertentdamage during rotation, a shroud 38 may be provided over an upperportion of the blade 40. The shroud may take any desired form. In theillustrated embodiment, the shroud covers an outer peripheral portion ofthe blade 40. The location of the shroud 38 should be selected to avoidany interference in measurement of the distance D by the sensor 50,discussed below.

[0028] If the blade 40 is properly mounted on the spindle 30, themounting face 42 of the blade 40 should rotate in a plane which issubstantially perpendicular to the rotational axis A-A of the spindle30. If the blade 40 is not properly clamped between the retaining nut 36and the mounting hub 34, however, the blade 40 may shift slightly as itcuts the wafer 12. This can lead to somewhat erratic movement of theperipheral cutting edge 46 of the blade 40, risking damage to the wafer12, as noted above.

[0029]FIG. 2 schematically illustrates another problem which may beencountered in mounting the blade 40 on the spindle 30. In FIG. 2, aburr B extends outwardly from the mounting face 35 of the mounting hub34 and abuts the mounting face 42 of the blade 40. (It should beunderstood that FIG. 2 is not drawn to scale and the size of the burr Bhas been exaggerated for purposes of illustration.) Such a burr B mayarise due to inadvertent damage to the mounting face 35 of the mountinghub 34 or to the blade 40. As shown in FIG. 2, the burr B prevents themounting face 42 of the blade 40 from lying flush against the mountingface 35 of the mounting hub 34. As a consequence, the blade 40 is notoriented perpendicular to the rotational axis (A-A in FIG. 1) of thespindle 30. As a consequence, the point of contact between theperipheral cutting edge 46 and the wafer 12 will shift from side to sideas the blade 40 is rotated. This can chip or otherwise damage the wafer12 being diced. While FIG. 2 schematically illustrates a burr B betweenthe mounting hub 34 and the blade 40, much the same situation can ariseif some foreign article becomes trapped between the blade 40 and themounting hub 34 as the blade 40 is mounted on the spindle 30.

[0030] The saw 10 of FIG. 1 also includes a sensor 50 which is adaptedto measure a distance of the blade 40 as the blade 40 rotates about therotational axis A-A. In one embodiment, the sensor 50 is adapted tomeasure the distance from the sensor 50 to the mounting face 42 of theblade 40 without any direct physical contact with the blade 40. This maybe accomplished, for example, by directing a beam of radiation at theblade 40 and measuring the reflection of that radiation by the blademounting face 42. Any of a variety of non-contact distance measurementdevices can be employed as the sensor 50 if they are suitably sensitive.In one useful embodiment of the invention, the sensor 50 comprises a CCDlaser displacement sensor, such as a LK-2500 series sensor availablefrom Keyence Corporation, Osaka, Japan.

[0031] The support 50 is adapted to maintain a fixed angularrelationship with respect to the rotational axis A-A of the spindle 30as the spindle 30 rotates about that axis A-A. In the embodiment of FIG.1, the sensor 50 is shown as being carried by the support 20. While thisensures that the angular relationship between the sensor 50 and therotational axis A-A remains fixed, it should be noted that the distancebetween the sensor 50 and the blade mounting face 42 will vary overtime, even if the blade is ideally mounted on the hub 34, as the spindle30 is translated inwardly and outwardly with respect to the support 20along the rotational axis A-A.

[0032] The sensor 50 is adapted to monitor the distance D from thesensor 50 to the blade mounting face 42. In one embodiment of theinvention, the sensor 50 monitors the distance D during the entireoperation of the saw 10 as it cuts the wafer 12. Cooling water on theblade mounting face 42 can interfere with accurate readings of thedistance D in some embodiments, though. In an alternative embodiment,the sensor 50 measures the distance D to the mounting face 42 only atselected times, as described below.

[0033]FIG. 4 schematically illustrates three idealized plots of thedistance D between the sensor 50 and the blade mounting face 42 forthree different circumstances. In an idealized condition wherein theblade mounting face 42 is perfectly flat and the blade 40 is perfectlymounted on the mounting hub 34, the distance D will not vary at all asthe blade 40 is rotated unless the spindle 30 is translated along therotational axis A-A. This idealized circumstance is represented by astraight line A in FIG. 4. The dashed curve C in FIG. 4 illustrates aplot of the distance D as a function of time t for an improperly mountedblade 40, such as the blade 40 shown in FIG. 2. This curve C isgenerally sinusoidal, with a period P which represents one completerevolution of the blade 40 about the rotational axis A-A. During thecourse of each period P, the distance D varies from a maximum reading toa minimum reading. This variation in the distance D may be considered avariance V_(c) for the curve C. The average distance D_(avg) of thecurve C may be thought of as a baseline distance from the sensor 50 tothe blade mounting face 42. The actual distance D will vary about thisbaseline distance D_(avg), as the blade rotates, with the maximum changefrom this baseline distance being a deviation D_(c) for the curve C.

[0034] If the variance V_(c) exceeds a predetermined maximum varianceV_(max), the blade 40 may be considered improperly mounted on thespindle 30. Likewise, if the deviation D_(c), of the curve C exceeds apredetermined maximum deviation D_(max), this can be taken as anindication that the blade 40 is likely improperly mounted on the spindle30. The maximum permitted variance V_(max), and/or deviation D_(max),may be selected to materially reduce the likelihood of inadvertentdamage to the wafer 12, while permitting reasonable tolerances in themounting hub 34, the blade 40, the spindle 30, and the fit of the blade40 on the hub 34. In one embodiment, for example, the maximum permittedvariance V_(max), is about 2 μm and the maximum permitted deviationD_(max) is about 1 μm.

[0035] The data from the sensor 50 may be delivered to the processor 60.The processor 60 may comprise any suitable structure which is adapted toprocess the signal from the sensor 50. For example, the processor 60 maycomprise a computer running a program adapted to process the signal fromthe sensor 50. If the processor 60 determines that the variance V_(c) asthe blade rotates exceeds the maximum permitted variance V_(max), or ifthe deviation D_(c) exceeds the maximum permitted deviation D_(max), theprocessor 60 may indicate an error condition. This can be communicatedin any desired fashion. For example, the processor may deliver a warningsignal to the operator on a display 62 connected to the processor 60.Alternatively or in addition to the output on the display 62, thewarning signal may comprise an audible and/or visible alarm signal on analarm 64 connected to the processor 60. This warning signal may bedesigned to get the attention of a human operator so the operator caninspect the saw 10 and intervene in its operation, if necessary. Inanother embodiment, the processor 60 is adapted to terminate rotation ofthe spindle 30 by the driver 22 if the variance V_(c) exceeds themaximum permitted variance V_(max), or if the deviation D_(c) exceedsthe predetermined maximum deviation D_(max). Terminating rotation of theblade 40 in this fashion can limit or prevent damage to the wafer 12 bycontact with an improperly mounted blade 40.

[0036]FIG. 4 shows an intermediate dotted curve B which schematicallyillustrates a blade 40 operating within acceptable operating parameters.The curve B is not a straight horizontal line representing no change atall in the distance D from the sensor 50 to the blade mounting face 42as in curve A. However, the variance V_(B) of the curve B is less thanthe maximum permitted variance V_(max). Similarly, the deviation D_(B)of the curve B is less than the maximum permitted deviation D_(max). Ifthe maximum permitted variance V_(max) and/or the maximum deviationD_(max) are appropriately selected, a blade 40 exhibiting a varianceV_(B) and a deviation D_(B) as shown in curve B can be used to cut thewafer 12 with little or no inadvertent damage to the wafer 12.

[0037]FIG. 3 schematically illustrates a relationship between theposition of the sensor 50 and the mounting surface 42 of the blade 40.For a given angular displacement of the blade 40 from a flush mountagainst the hub mounting face (35 in FIG. 2), the variation in thedistance (D in FIG. 1) between the sensor 50 and the blade mountingsurface 42 will depend on the location of the target area 52 of thesensor 50 on the blade mounting surface 42. If the sensor 50 is orientedto detect the distance to a target area 52 positioned adjacent theperipheral cutting edge 46 of the blade 40, the change in the distance Dwill be at or near its maximum for a given angular displacement of theblade 40 from a flush mount against the hub 34. If the sensor is insteadoriented toward a target area 52′ positioned closer to the center of theblade, the variation in the distance D between the sensor 50 and themounting face 42 at that location will vary less for the same angulardisplacement of the blade 40 from a proper mounting position. If thesensor is adapted to move with the spindle 30 as the spindle rotationalaxis A-A moves with respect to the wafer table 14, the sensor 50 willalways be oriented toward the same target area 52 on the blade mountingface 42. If, however, the sensor remains stationary as the distancebetween the axis A-A and the wafer table 14 is varied, the sensor targetlocation 52 on the blade mounting face 42 will vary. If the processormonitors the relative position of the spindle 30 to the wafer table 14over time, however, the processor can determine the radius of the sensortarget area 52 from the center of the blade 40 and adjust the acceptableoperating parameters accordingly. Hence, the maximum permitted varianceV_(max) and the maximum permitted deviation D_(max) will be less for thetarget area 52′ with a radius R₂ from the center of the blade 40 thanthey will be for the target area 52 with a larger radius R₁.

[0038] Dual-Blade Saw

[0039]FIGS. 5 and 6 schematically illustrate a twin spindle dual-bladesemiconductor substrate saw 110 in accordance with an alternativeembodiment of the invention. The structure and operation of this saw 110bears significant resemblance to the structure and operation of the saw10 shown in FIGS. 1-3. Two distinctions between these two designs areworth noting, though. First, the saw 110 of FIG. 5 has a pair of blades140 a and 140 b rather than a single blade 40. Second, the sensors 150 aand 150 b of the saw 110 are adapted to move with respect to thesupports 120 a and 120 b rather than being permanently affixed to thesupport 20.

[0040] The saw 110 of FIGS. 5 and 6 is shown as having a pair ofsupports 120 a and 120 b, each of which houses a separate driver 122 aand 122 b. If so desired, both of the spindles 130 a and 130 b may becoupled to a common driver 122 and/or supported by a common support 120.If separate drivers 122 a-b are utilized, their operation can becoordinated by the processor 160.

[0041] As with the prior embodiment, a first spindle 130 a may comprisea shaft 132 a, a mounting hub 134 a and a retaining nut 136 a formounting the first blade 140 a. Similarly, a second spindle 130 b mayinclude a shaft 132 b, a mounting hub 134 b, and a retaining nut 136 bto mount the second blade 140 b.

[0042] A wafer table 114 may position a wafer 112 in proximity to theblades 140 a-b so the blades 140 a-b can make a cut in the wafer 112.(Four such cuts, designated by reference numerals 1-4, are schematicallyshown in FIG. 6.) In FIGS. 5 and 6, each of the blades 140 a-b is shownas having a separate water line 116 a or 116 b. If desired, a singlewater line can be used to deliver a flow of water or other coolingliquid to both of the blades 140.

[0043] The dual-blade saw 110 of FIGS. 5 and 6 utilizes a separatesensor 150 a or 150 b to measure a distance to an associated one of theblades 140 a or 140 b, respectively. If so desired, one or both of thesesensors 150 a-b can be carried by the support 120 a or 120 b associatedwith the blade 140 a or 140 b toward which the sensor 150 a or 150 b,respectively, is directed. In the illustrated embodiment, however, thesensor 150 a or 150 b for each blade 140 a or 140 b is carried by theshroud 138 b or 138 a for the opposite blade 140 b or 140 a. Inparticular, the shroud 138 a associated with the first blade 140 acarries the second sensor 150 b for measuring a distance to the outerface 144 b of the second blade 140 b. Similarly, the second shroud 138 bcarries the first sensor 150 a for measuring a distance to the outerface 144 a of the first blade 140 a.

[0044] The sensors 150 a-b can be mounted on their respective shrouds138 b-a in any desired fashion and in any suitable location. In theillustrated embodiment, the first sensor 150 a is attached to the secondshroud 138 b via an L-shaped bracket 152 a. This bracket 152 a ispositioned toward one edge of the shroud 138 b and extends downwardlybeyond the bottom edge of the opposite shroud 138 a. This orients thefirst sensor 150 a toward a target area adjacent a periphery of theouter face 144 a of the first blade 140 a. The other sensor 150 b can bemounted to the other shroud 138 a using a similar L-shaped bracket 152b. To avoid any interference between the two sensors 150 a-b, the secondsensor 150 b may be positioned on the opposite side of the sharedrotational axis A-A of the spindles 130 a-b (see FIG. 6).

[0045] As the saw 110 is operated, it may be desirable to alter thedistance between the first blade 140 a and the second blade 140 b toproperly align the blades 140 along separate streets on the wafer. Thisdistance can be varied by moving one or both of the spindlestransversely along their coincident axes. The sensors 150 a-b arecarried on shrouds 138 a-b which are, in turn, carried by the spindles130 a-b. Accordingly, as the spindles 130 move to alter the distancebetween the blades 140, the distance from the sensors 150 a-b to theirrespective blades 140 a-b will be altered, as well.

[0046] Data from both of the sensors 150 a-b can be delivered to acommon processor 160. Aspects of performance of the blades 140 a-b canbe displayed on the display 162. If the distances measured by thesensors 150 a-b fall outside of acceptable operating parameters, awarning signal can be delivered to the operator via an alarm 164.Instead of or in addition to delivering such a warning signal to thealarm 164, the processor 160 may terminate rotation of one or both ofthe spindles 130 a-b. In one embodiment, the processor 160 terminatesrotation only of the spindle 130 a or 130 b carrying the blade 140 a or140 b which falls outside of acceptable operating parameters. In analternative embodiment, the processor 160 terminates rotation of bothspindles 130 a-b if the data from the sensors 150 a-b indicates thateither one of the blades 140 a-b is operating outside of acceptableoperation parameters.

[0047] Methods of Operation

[0048] The present invention provides a variety of methods for utilizinga semiconductor substrate saw. For purposes of illustration, referenceis made in the following discussion to the saw 110 shown in FIGS. 5 and6. It should be understood, though, that this is intended solely to aidin understanding the methods and that methods of the invention may becarried out using devices which differ materially from the saw 110 ofFIGS. 5 and 6.

[0049] One or both of the blades 140 a-b will be replaced with a newblade as they near the end of their useful life. Often, both of theblades 140 a-b will be replaced at the same time, but it may benecessary to replace one of the blades, such as one of the blades isdamaged. To replace the first blade 140 a, the retaining nut 136 a maybe loosened and the shroud 138 may be lifted out of the way. The usermay then slide the used first blade 140 a off the spindle 130 a. A newfirst blade 140 a may be positioned on the spindle 130 a, the retainingnut 136 a may be tightened to hold the new first blade 140 a on thespindle 136 a, and the shroud 138 a may be placed back in its originalposition about an outer peripheral portion of the first blade 140 a. Thesecond blade 140 b may be replaced in much the same fashion.

[0050] Once the new blade 140 is mounted on its spindle 130, the shaft132 of the spindle 130 may be rotated. In one embodiment, both of theshafts 132 a-b are rotated at the same time even if only one of theblades 140 a-b has been replaced. As the blades 140 a-b are rotated, thedistance from the sensor 150 a to the outer face 144 a of the firstblade 140 a may be monitored and the distance from the second sensor 150b to the outer face 144 b of the second blade 140 b may be monitored.The processor 160 may receive data from the sensors 150 a-b anddetermine the variance and/or deviation for each of the blades 140 a-bgenerally as outlined above in connection with FIG. 4. If the varianceand/or deviation of either of the blades 140 a-b exceeds thepredetermined maximum value V_(max) or D_(max), respectively theprocessor 160 may indicate an error on the display 162 or via the alarm164. Alternatively or in addition to indicating such an error, theprocessor 160 may terminate rotation of one or both of the blades 140a-b.

[0051] The blades 140 a-b may be replaced with the spindles 130 a-bspaced sufficiently above the wafer table 114 to space the peripheralcutting edges 146 a-b of the blades 140 a-b above the surface of anywafer 112 in the wafer table 114. In one embodiment, the blades 140 a-bare rotated with the spindles 130 a-b in these elevated positions andbefore the newly mounted blade(s) are lowered into contact with a wafer112. This will help identify any problems with the mounting of theblades 140 a-b before an improperly mounted blade 140 a-b is allowed todamage the wafer 112. In one adaptation of this method, the first andsecond blades 140 a-b are lowered into contact with the wafer 112 onlyif the blades 140 a-b are operating within acceptable parameters and theprocessor 160 does not indicate any error. Rather than leaving thisfunction entirely to the processor 160, the processor 160 may simplyindicate any error to an operator and the operator can determine whetherto lower the blades 140 a-b into cutting contact with the wafer 112.

[0052] In cutting the wafer 112, the peripheral cutting edges 146 a-b ofboth of the rotating blades 140 a-b can be brought into contact with asurface of the wafer 112. By controlling the distance of the spindles130 a-b from the wafer table 114, the depth of the cuts by the blades140 a-b can be controlled. In some circumstances it may be desirable tocut only partially through the wafer 112 rather than through its entirethickness. After the partial cut has been made, the wafer 112 may bebroken along the kerfs left by the blades 140 a-b.

[0053] Depending on the nature of the sensors 150, an undue amount offluid on the outer faces 144 of the blades 140 may interfere withprecise measurement of the distance to the blade outer face 144. Hence,in one embodiment, the new blades 140 a and 140 b are rotated and thedistance is monitored using the sensors 150 before the blades 140 arebrought into contact with a flow of water or other cooling liquid fromthe water lines 116 a-b.

[0054] It may be desirable to check the status of the blades 140 a-bfrom time to time to ensure that they remain properly mounted on theirrespective spindles 130 a-b. It may be possible to monitor the distancefrom each sensor 150 a-b to its associated blade 140 a-b while the bladeis used to cut a wafer 112. In an embodiment of the invention, however,the processor will indicate an error and/or terminate rotation of theblades only when the blades are not cutting a wafer 112. In accordancewith one specific embodiment, the spindles 130 a-b are moved away fromthe wafer table 114 to space the peripheral cutting edges 146 of theblades 140 from the wafer 112. The spindles 130 may be returned to thesame position with respect to the wafer table 114 they occupied when thenew blades 140 were installed on the spindles 130. In an alternativeembodiment, the blades 140 may be mounted on their respective spindles130 at a first elevation and the proper mounting of the blades 140 onthe spindles 130 may be confirmed before the spindles are lowered towardthe wafer 112. The later confirmation that the blades 140 remainproperly mounted can be performed at a different elevation, such as at aposition closer to the wafer table 114. In one embodiment, the blades140 are spaced sufficiently from the wafer table 114 and the water lines116 to ensure that the blades are not in contact with a continuous flowof the cooling liquid. At this elevation, the spindles 130 may berotated and the distance from each of the sensors 150 a-b to theirrespective blades 140 a-b can be monitored.

[0055] The processor 160 may preclude lowering the blades 140 back intocontact with the wafer 112 if the second mounting check finds that themeasured distances to the blades 140 no longer fall within acceptableoperating parameters. It may be possible to perform a second check aftermaking a first series of cuts in the wafer 112 without interfering withnormal operation of the saw 110. For example, it is common practice inthe industry to check the cuts or kerfs (1-4 in FIG. 6) already formedin the wafer 112 from time to time to ensure that the wafer 112 is beingdiced properly. The interim, post-cutting measurement of the blademounting using the sensors 150 can be performed during such a routinelull in cutting.

[0056] In one embodiment of the invention, both of the blades 140 arereturned to a specific, pre-defined location each time the mounting ofthe blades 140 is to be checked with the sensors 150. Returning to aspecific location each time is not required, though. The variance anddeviation measurements help identify irregularities in the motion of theblade as it rotates and these measurements are independent of the actualbaseline distance (D_(avg) in FIG. 4). As a consequence, an improperlymounted blade can be identified even if the baseline distance D_(avg)between a sensor 150 a-b and the associated blade 140 a-b differs fromone measurement to the next. As a consequence, the distance between theblades 140 a-b. can be varied to cut along different streets on thewafer 112 and the mounting of the blades 140 can be checked withouthaving to return the blades to a home position. In the single-blade saw10 of FIG. 1, the mounting of the blade 40 on the spindle 30 can bechecked without having to move the blade 40 to a specific location withrespect to the support 20. The ability to check the mounting of theblades 140 a-b or 40 without returning them to a fixed position eachtime eliminates additional blade movements, helping ensure more preciseregistration of the blades 140 or 40 with the streets on the wafer 112.

[0057] From the foregoing, it will be appreciated that specificembodiments of the invention have been described herein for purposes ofillustration, but that various modifications may be made withoutdeviating from the spirit and scope of the invention. Accordingly, theinvention is not limited except as by the appended claims.

1. A method of cutting a semiconductor substrate, comprising:positioning the semiconductor substrate with respect to a blade of asaw; rotating the blade in a first spaced position wherein a peripheralcutting edge of the blade is spaced from the semiconductor substrate;measuring a distance to a face of the blade as the blade is rotated inthe first spaced position and determining a first variance in themeasured distance as the blade is rotated; and, if the first variance isno greater than a predetermined maximum variance, contacting thesemiconductor substrate with the peripheral cutting edge of the bladeand translating the blade with respect to the semiconductor substrate tocut at least partially through the semiconductor substrate.
 2. Themethod of claim 1 further comprising terminating rotation of the bladeif the first variance is greater than the predetermined maximumvariance.
 3. The method of claim 1 further comprising generating awarning if the first variance is greater than the predetermined maximumvariance.
 4. The method of claim 1 wherein the first variance isdetermined without contacting the blade with a flow of cooling liquid.5. The method of claim 4 wherein the blade is contacted with a flow ofcooling liquid when the blade is cutting the semiconductor substrate. 6.The method of claim 1 wherein the blade is rotated in the first positionprior to contacting the semiconductor substrate with the blade.
 7. Themethod of claim 1 further comprising positioning the blade in a secondspaced position after cutting the semiconductor substrate, theperipheral cutting edge of the blade being spaced from the semiconductorsubstrate when the blade is in the second spaced position; rotating theblade in the second spaced position without cutting the semiconductorsubstrate; measuring the distance to the face of the blade as the bladeis rotated in the second spaced position and determining a secondvariance.
 8. The method of claim 7 wherein the first spaced position isthe same position as the second spaced position.
 9. The method of claim7 further comprising contacting the semiconductor substrate with theperipheral cutting edge of the blade if the second variance is nogreater than the predetermined maximum variance.
 10. The method of claim7 further comprising terminating rotation of the blade if the secondvariance is greater than the predetermined maximum variance.
 11. Themethod of claim 7 further comprising generating a warning if the secondvariance is greater than the predetermined maximum variance.
 12. Amethod of operating a semiconductor substrate saw, comprising: rotatinga blade of the saw without contacting the blade with a flow of liquid;monitoring a distance to a face of the blade as the blade rotates;determining a first baseline distance to the face of the blade anddetermining a first deviation from the baseline distance; indicating anerror if the first deviation is greater than a predetermined maximumdeviation; and, only if the error is not indicated, making a first cutat least partially through a semiconductor substrate with the bladewhile contacting the blade with a flow of liquid.
 13. The method ofclaim 12 further comprising terminating rotation of the blade if anerror is indicated.
 14. The method of claim 12 further comprisinggenerating a warning if an error is indicated.
 15. The method of claim12 wherein the first cut is made by contacting the semiconductorsubstrate with a peripheral cutting edge of the blade.
 16. The method ofclaim 15 wherein the liquid comprises water.
 17. The method of claim 12wherein the distance to the face of the blade is monitored when theblade is in a first position, the blade in the first position beingspaced from the semiconductor substrate.
 18. The method of claim 12further comprising positioning the blade in a spaced position with aperipheral cutting edge of the blade spaced from the semiconductorsubstrate; rotating the blade in the spaced position without cutting thesemiconductor substrate; monitoring a distance to the face of the bladeas the blade is rotated in the spaced position; and determining a secondbaseline distance to the face of the blade and determining a seconddeviation from the baseline distance.
 19. The method of claim 18 furthercomprising making a second cut at least partially through thesemiconductor substrate only if the second deviation is no greater thanthe predetermined maximum deviation.
 20. The method of claim 18 furthercomprising terminating rotation of the blade if the second deviation isgreater than the predetermined maximum deviation.
 21. The method ofclaim 18 further comprising generating a warning if the second deviationis greater than the predetermined maximum deviation.
 22. A method ofexchanging a blade of a semiconductor substrate saw, comprising:removing a used blade from a blade mount carried on a shaft of the saw;mounting a new blade on the blade mount; prior to contacting asemiconductor substrate with the new blade, rotating the new blade;prior to contacting the semiconductor substrate with the new blade,monitoring a distance to a face of the new blade as the blade rotates;prior to contacting the semiconductor substrate with the new blade,determining a baseline distance to the face of the blade and determininga deviation from the baseline distance; prior to contacting thesemiconductor substrate with the new blade, indicating an error if thedeviation exceeds a predetermined maximum deviation; and, only if theerror is not indicated, making a cut at least partially through thesemiconductor substrate with the blade.
 23. A method of exchanging ablade of a multiple-blade semiconductor substrate saw which includes aused first blade and a second blade, the used first blade being carriedon a first shaft for rotation with the first shaft and the second bladebeing carried on a second shaft for rotation with the second shaft, themethod comprising: removing the used first blade from the first blademount; mounting a new first blade on the first blade mount; rotating thenew first blade in a first position; monitoring a distance from a firstsensor to a face of the new first blade as the new first blade rotatesin the first position, the first sensor being associated with the secondshaft; indicating whether a first variance in the monitored distance asthe new first blade is rotated is greater than a predetermined maximumfirst variance; and, if the first variance is not greater than themaximum first variance, contacting a semiconductor substrate with thenew first blade and with the second blade.
 24. The method of claim 23further comprising moving the second shaft and the first sensorlaterally with respect to the first shaft, thereby changing the distancefrom the first sensor to the face of the new first blade.
 25. The methodof claim 23 further comprising terminating rotation of the blade if thefirst variance is greater than the predetermined maximum variance. 26.The method of claim 23 further comprising generating a warning if thefirst variance is greater than the predetermined maximum variance. 27.The method of claim 23 wherein the first variance is determined withoutcontacting the blade with a flow of cooling liquid.
 28. The method ofclaim 27 wherein the blade is contacted with a flow of cooling liquidwhen the blade is cutting the semiconductor substrate.
 29. The method ofclaim 28 wherein the cooling liquid comprises water.
 30. The method ofclaim 23 wherein the blade is rotated in the first position prior tocontacting the semiconductor substrate with the blade.
 31. The method ofclaim 23 further comprising cutting at least partially through thesemiconductor substrate with the new first blade and with the secondblade.
 32. The method of claim 31 further comprising, after cutting thesemiconductor substrate, rotating the new first blade in a secondposition, monitoring the distance from the first sensor to the face ofthe new first blade as the new first blade rotates in the secondposition, and indicating whether a second variance in the monitoreddistance as the new first blade is rotated is greater than apredetermined maximum second variance.
 33. The method of claim 32wherein the first position differs from the second position.
 34. Themethod of claim 32 further comprising moving the second shaft and thefirst sensor laterally with respect to the first shaft, thereby changingthe distance from the first sensor to the face of the new first blade,after monitoring the first distance and before monitoring the seconddistance.
 35. The method of claim 23 further comprising removing thesecond blade from the second mount; mounting a new second blade on thesecond blade mount; rotating the new second blade; monitoring a distancefrom a second sensor to a face of the new second blade as the new secondblade rotates, the second sensor being associated with the first shaft;and indicating whether a second variance in the measured distance as thenew second blade is rotated in the second position is greater than apredetermined maximum second variance.
 36. The method of claim 35wherein the semiconductor substrate is contacted with the first bladeand with the second blade only if the first variance is not greater thanthe maximum first variance and the second variance is not greater thanthe maximum second variance.
 37. The method of claim 35 wherein themaximum first variance is equal to the maximum second variance and thesemiconductor substrate is contacted with the first blade and with thesecond blade only if neither the first variance nor the second varianceis greater than the maximum first variance.
 38. A semiconductor wafersaw, comprising: a carrier for a microelectronic workpiece; a driver; afirst shaft coupled to the driver and extending opposite the carrier,the first shaft having a first axis; a first blade mount carriedadjacent an end of the shaft for rotation with the first shaft; a firstblade carried by the first blade mount for rotation with the first blademount, the first blade having a face and a peripheral cutting edge; asensor spaced from the first blade and oriented toward the face of thefirst blade, the sensor maintaining a fixed angular position withrespect to the first axis as the first blade is rotated with the shaft,the sensor being adapted to measure a distance to the face of the firstblade; and a processor operatively coupled to the sensor, the processorbeing adapted to indicate if the distance to the face of the first bladedeviates more than a predetermined permitted deviation from a baselinedistance to the face of the first blade as the blade rotates.
 39. Thesemiconductor wafer saw of claim 38 wherein the sensor comprises a CCDlaser displacement sensor.
 40. The semiconductor wafer saw of claim 38wherein the first shaft is adapted to move transversely with respect tothe sensor.
 41. The semiconductor wafer saw of claim 38 wherein thesensor is carried by a support and the first shaft is moveablevertically with respect to the support.
 42. The semiconductor wafer sawof claim 41 wherein the first shaft is moveable transversely withrespect to the support to vary the baseline distance.
 43. Thesemiconductor wafer saw of claim 38 wherein first shaft is moveable withrespect to the sensor to vary the baseline distance.
 44. Thesemiconductor wafer saw of claim 38 further comprising a cooling liquidsupply line positioned to deliver a cooling fluid, the processor beingadapted to control flow through the supply line to terminate flow ofcooling fluid when the sensor monitors a the distance to the face of thefirst blade.
 45. A semiconductor wafer saw, comprising: a carrier for amicroelectronic workpiece; a first spindle extending opposite thecarrier, the first spindle having a first axis; a first blade carried bythe first spindle for rotation with the first spindle, the first bladehaving a face and a peripheral cutting edge; a second spindle extendingopposite the carrier, the second spindle having a second axis; a secondblade carried by the second spindle for rotation with the secondspindle, the second blade having a face and a peripheral cutting edge; afirst sensor carried by the second spindle and adapted to measure afirst distance to the face of the first blade, the first sensormaintaining a fixed angular position with respect to the first axis asthe first blade rotates about the first axis; a second sensor carried bythe first spindle and adapted to measure a second distance to the faceof the second blade, the second sensor maintaining a fixed angularposition with respect to the second axis as the second blade rotatesabout the second axis; and a processor operatively coupled to the firstand second sensors, the processor being adapted to indicate if variationof the first distance as the first blade rotates exceeds a predeterminedmaximum first variation and to indicate if variation of the seconddistance as the second blade rotates exceeds a predetermined maximumsecond variation.
 46. The semiconductor wafer saw of claim 45 whereinthe first axis coincides with the second axis.
 47. The semiconductorwafer saw of claim 46 wherein one or both of the first and secondspindles are adapted for movement transversely along the coincidentfirst and second axes.
 48. The semiconductor wafer saw of claim 45wherein the first spindle is adapted for movement transversely along thefirst axis, movement of the first spindle along the first axis varying abaseline distance of the first sensor from the face of the first blade.49. The semiconductor wafer saw of claim 48 wherein the second spindleis adapted for movement transversely along the second axis.
 50. Thesemiconductor wafer saw of claim 45 wherein the second spindle isadapted for movement transversely along the second axis, movement of thesecond spindle along the second axis varying a baseline distance of thesecond sensor from the face of the second blade.
 51. The semiconductorwafer saw of claim 45 wherein the first spindle is adapted for movementtransversely along the first axis and the second spindle is adapted formovement transversely along the second axis.
 52. The semiconductor wafersaw of claim 45 wherein the first sensor comprises a CCD laserdisplacement sensor.
 53. The semiconductor wafer saw of claim 45 whereinthe second sensor comprises a CCD laser displacement sensor.
 54. Thesemiconductor wafer saw of claim 45 wherein the first and secondspindles are each moveable vertically with respect to the carrier. 55.The semiconductor wafer saw of claim 45 further comprising a coolingliquid supply line positioned to deliver a cooling fluid, the processorbeing adapted to control flow through the supply line to terminate flowof cooling fluid when the sensor monitors a the distance to the face ofthe first blade.